Spliced abrasive belt, band, and the like



Dec. 25, E945. J MlLLER ET AL 2,391,731

SPLICED ABRASIVE BELT, BAND, AND THE LIKE Filed May 17, 1943 Patented Dec. 25, 1945 SPLICE!) ABRASIVELIBkEgI, BAND, AND THE Theodore J. Miller, St. Paul, and Richard G. Riedesel, North St. Paul, Minn., assignors to Minnesota Mining 8: Manufacturing Company, St. Paul, Minn, a corporation of Delaware Application May 17, 1943, Serial No. 487,228

16 Claims.

This invention relates to the joining of two portions of sheet material, especially abrasive sheet material, in a manner to enable the joint to withstand tensile and shearing stresses while at the same time maintaining the thickness of the joint substantially the same as the thickness of the material being joined; and to useful articles of manufacture produced thereby.

More specifically this invention is directed to the joining of the edges or ends of abrasive coated sheet material to form abrasive articles such as belts, sleeves and the like in which the joint is of suflicient strength to resist the stresses imposed upon the article when used for abrading purposes, while at the same time normally providing an uninterrupted abrading surface across the joint substantially umnodified from that of the remainder of the article, and/or in which the thickness of the material at the joint or splice is substantially the same as the thickness of the abrasive coated material from which the article is formed.

Abrasive coated sheet material used for making abrasive articles comprises essentially a backing of sheet material, one surface of which is coated with abrasive grits bonded to said backing sheet by an adhesive. The backing sheet is commonly of woven fabric such as cloth or of felted fabric such as paper or felt, but may be of any sheet material, either fibrous or non-fibrous or combinations thereof. Examples of non-fibrous materials are films of cellulose material such as cellulose acetate and regenerated cellulose commonly known as Cellophane, or may be sheets of various other film forming materials such as rubber, synthetic resins or derivatives or modifications thereof. Where fibrous sheet materials, either woven materials such as cloth or unwoven materials such as paper, are used these may be treated by coating or impregnating with materials such as glue, rubber or compositions or derivatives of rubber, natural or synthetic resins, various drying oils, or combinations of the above with each other, to impart various properties such as strength, toughness, flexibility, stiffness, resistance to water or to oil, or other properties which may be desirable for any particular use or conditions of use for which the abrasive material may be intended. The present invention is directed to making joints or splices of any sheet material which ossesses the characteristics of compressibility and/or flow under pressure, and is also directed to the improved articles or products made in accordance herewith.

The abrasive grits may be of any suitable material of which examples are, aluminum oxide, silicon carbide, garnet, flint, emery, synthetic abrasive grains, etc. The adhesive for binding the abrasive grits to the backing may be glue, casein, natural or synthetic resins either alone or combined with drying or semi-drying oils to form varnish or lacquers, various cellulosic compounds such as nitro-cellulose, inorganic adhesives such as sodium silicate or any desired combination of the above materials found to give the various desirable properties in the coated abrasive sheet. Examples of binders or bonding adhesives are given in various patents and pending applications, such as Carlton and Oakes Patent No. 2,230,934 and Cakes application Serial No. 293,192, and these exemplary disclosures are incorporated by reference. The nature of the binder coat of adhesive holding the abrasive grits to the backing sheet and the nature of any treatments given to the backing sheet are of importance to the present invention only insofar as they may afiect the necessity for the use of an adhesive in forming the splice as hereinafter described or as they may afiect the nature of such adhesive material when used, or the compressibility or character of the coated abrasive sheet material as a. whole.

In making abrasive articles such as belts or sleeves from abrasive coated material as above described, which require the joining or splicing of edges or ends of such material, it is desirable that the joints or splices be such as to afford a smooth finished surface without substantial alteration of the abrasive coating and that the thickness of the article at the splices be substantially the same as that of the main portion of the material. This is especially important with abrasive belts or sleeves to be used for fine, precision grinding or polishing, but is also important in abrasive belts, sleeves, etc., generally, even where they are not used for precision work or fine finishing. It is also necessary that such splices have sufficient strength to resist the stresses imposed upon the article in use. In past practice joints or splices have been made, for example, by skiving the adjacent edges by removing the abrasive coating from one or both edges and adhesively uniting the backing sheets in overlapped position. In all such forms the skived splice failed to give the desired results, either by reason or resulting in a splice from which the abrasive had been removed, and/or by failure to produce a joint of sumcient strength by reason of weakening of the backing sheet, and/or because the spliced joint was of a different or greater thickness than the remainder of the abrasive belt, abrasive sleeves,

etc., and caused a bumping or thumping, with consequently non-uniform grinding or abrading during use. Furthermore the skiving operation results in substantial waste of the abrasive coated sheet material.

Where butt" joints or splices have heretofore been made by abutting the edges of the sheet material and uniting them with a strip of ,sheet material adhered to the back surface of the abrasive belt, etc., to form a splice, the sheet material used for such splicing strip has heretofore been of material similar to the backing material and of substantial thickness. Thus the thickness of the belt or sleeve at the splice has been greater than elsewhere, thus lacking the desirable substantial uniformity of thickness throughout the length of the belt.

For grinding operations where uniformity of abrasive surface and of thickness of the belt or sleeve was essential, it has heretofore been the practice to apply the abrasive coated sheet material to a complete liner element in which the respective joints of the liner element and of the abrasive coated material have been at separate points. This is, however, an expensive procedurc, not only with respect to materials but also with respect to cost of manufacture. Additionally it decreases the flexibility of the abrasive belt, with a consequent decrease of usefulness for various purposes.

It is therefore an object of this invention to provide an abrasive belt, sleeve or the like having a joint or splice wherein the adjacent edges will be in abutting relation to each other and whereby one surface of the sheet material will be unaltered at the joint or splice.

It is a further object of this invention to provide a butt joint or splice for abrasive coated articles such as belts and sleeves, wherein the abrasive coated surface at the joint is unaltered and the thickness of the composite sheet at the splice is substantially the same as elsewhere in the article.

A further object is to provide a splice, preferably having the above desirable qualities, which develops all, or at least the greater proportion of the strength of the material spliced, across the belt or sleeve. Leaded iron wire and brass and bronze wire have been found to be usitable for this p rp se. We have also found that threads spun from glass filaments are suitable for this purpose. In general, in addition to having the general characteristics above discussed, such material is most commonly relatively incompressible, in relation to the backing of the sheeted abrasive or sandpaper.

Due to the much greater unit tensile strength of the wires or threads as compared with that of the backing material, the aggregate sectional area of these wires or threads required to develop a tensile strength equal to that of the backing ma terial, for any given width of belt or sleeve. is

only a small fraction of the sectional area of the backing material at the splice. Such wire or threads can therefore be positioned across the joint in the direction of the stresses to be transferred and by reason of the relatively small aggregate volume of such wires or threads, as compared with the volume of the backing material, and the compressible nature of said backing material, the wires or threads can be embedded under pressure in the backing material without increasing the total thickness of the material at the joint. Such wires or filaments extend a sufficient distance each way from the joint to effect the transfer of the stress from the backing material to the wires or filaments and are embedded in and adhesively bonded to said backing material either by the material itself or by an adhesive supplied for that purpose. The diameter of the wires or filaments are selected with reference to the thickness of the backing material and are never greater than such thickness and preferably should be substantially less. For convenience in fabrication, as well as advantages in use, we have found it preferable to utilize the metal. wires in the form of woven metal cloth of relatively coarse mesh. In

joint thereof. These and other objects and advantages will be apparent from the description taken as a whole.

The present invention provides a method for joining the abutting edges of abrasive coated sheet material to form abrasive articles such as belts, sleeves or the like wherein the thickness of the sheet material at the splice is substantially that of the abrasive sheet material elsewhere in the article and in which the abrasive coated surface is substantially unaltered at the area of the splice. The employment of the method of this invention further results in the production of a new article of-manufacture in the nature of abrasive belts and abrasive sleeves and the like not heretofore known.

In providing the above described improved abrasive belts and sleeves we have found that a splice having the desired characteristics can be formed by the use as a splicing material of sheet material including fine strands of material having a high unit tensile strength relative to that of the backing material of the abrasive coated sheet. Specific examples of such materials are metals such as iron, steel, steel alloys, brass or other metals or alloys of high tensile strength and also of sufficient resiliency to resist the repeated this form the wires are more readily handled and also the cross wires serve to enhance the transfer of stress from the backing material to the wires and provide a joint which is firm and highly resistant to disruption during handling or because ofside stresses. Similarly we have found it normally to be most convenient to use glass filaments in the form of glass cloth. Where metal or glass cloth is used it is of course necessary to select such material where the combined thickness of the wires or filaments forming the warp and the woof of the metal or glass cloth shall not exceed the thickness of the backing material. Since in general the principal stress to be taken by the splicing material is in one direction, the wires or threads can be of greater size in the direction of the principal stress and of lesser size in the other direction, thus making a stronger element in the direction of the greatest stress while desirably reducing the total thickness of the material. Also, we contemplate the use of a wire screen (e. g. with similar sized wires running in both directions) for reinforcing the joint byhaving the 'wires of the screen at an angle of the order of 45' to the length of the belt or the circumference of the band, thus providing a greater number of wires across an approximately transverse Joint. As a further alternative we have found that the metal wires or glass threads may be embedded in a film of adhesive, e. g. such as glue or resin, to facilitate the handling and also to supply the necessary adhesive material, where such is needed.

The length of the wires or threads either as such Or in the woven cloth or adhesive film depends upon the strength of the backing material and the amount of the stress to be transferred across the joint. It varies from as little as 541 01 an inch, or less, for light belts or sleeves up to 1% inches, or more. for heavy belts, and up to several inches for sleeves. In some cases, in abrasive belts and sleeves, strands of wire or the like may be embedded in and extend around the entire backing, with the ends of the strands of wire terminating at different points. If this latter embodiment is employed, it is often desirable to employ a relatively thin or open meshbacking, or sometimes no backing at all, i. e. so-called backless sandpaper, the wire strands or threads furnishing strength and support to the sheeted abrasive material.

In abrasive belts or sleeves the joints may be substantially normal to the direction of travel or may be at any desired angle thereto. Additionally, if desired, the jointmay be in the form of a series of points or of interlocking areas altho usually such construction is not required because of the intimate and permanent union secured between the splicing material and the backing material by the construction of this invention.

In practicing the method of this invention the edges to be joined are first cut to the desired lines and then placed on a fiat surface in abutting relation, with the surface which is not coated with abrasive exposed. A coating of adhesive is then applied over the area of said surface to be covered by the splicing material and the strip of splicing material applied. The entire area of the splice is then subjected to pressure sufficient to press the wires or threads of the splicing material into the backing material. The pressure can be supplied in any convenient form of press and where the adhesive used is of a heat setting nature, the plates of the press can be heated to set the adhesive. In certain cases where the abrasive coating might be crushed or. injured by the pressure it has been found desirable to use a sheet of soft material such as paper, rubber, cloth, etc., under the abrasive coated side during the application of the pressure. By the application of sufllcient pressure, the splicing material of metal wires or glass threads or the like will be forced completely into the substance of the backing sheet and the backing sheet compressed to an extent such that the thickness of the combined material at the area of the splice is essentially no greater than that of the rest of the abrasive In some cases where the backing has been impregnated or coated such treatment may supply all the adhesive required to secure thesplicing element to the backing. Also as above suggested, the wires of the splicing element may b preliminarily placed in a fllm of the adhesive in which case the splicing material supplies its own adhesive.

By reason of the relatively small volume of the splicing material as compared with the volume of the backing sheet we have found that in splices made as above described the properties 01' the area of the splice, which aifect the performance in use of the abrasive article, are substantially the same as those of the rest of the area of the article.

While splices as heretofore described have been found to :be a marked improvement over the prior practice in abrasive articles such as abrasive belts, sleeves, cones, etc., made from abrasive coated sheet material, yet they have been found to be particularly adapted to the production of a special form of abrasive sleeve known as "spiral wound sleeves. These sleeves are made by winding strips of abrasive coated material into a continuous cylinder, from which cylindrical pieces of suitable lengths are subsequently cut. In the prior practice the abrasive material was wound upon a supporting layer of material in order to enable the use of abutting joints which are essential in an article of this type. By the use of the present invention these sleeves have been formed in continuous lengths by feeding strips of the splicing material onto a forming mandrel and then applying the strip of abrasive material from a supply thereof, applying adhesive to each edge of the backing, placing the strips over the previously applied strip of splicing material so positioned that the joint between the successive convolutions of abrasive coated material falls in the vstrip using the forming mandrel as the other coated material. Even with thin abrasive belts of fine grit sizes we can readily produce our splice while keeping the thickness of the splice within .002 inch or less of the thickness of the rest of the belt (without skiving or grinding down the mineral coating at the splice), and commonly we can control the thickness of the splice so that it is the same as that of the rest of the belt. It will be understood that a variation in thickness of .002, .001 or .0005 inch between the splice and the rest of the belt, attainable by our invention, is very minute, even in connection with the precision grinding of radio crystals, and other precision grinding, for which our continuous belts are highly useful.

The selection of the adhesive used will depend upon the material, if any, used for coating or impregnating the backing sheet and also upon the use to which the belt or sleeve is intended to serve. Any suitable material such as hereinabove mentioned for use as coating or impregnating for the backing, or as the binder to bond the abrasive grits to the backing, may be used.

center of the splicing strip and then applying pressure to the outer surface of the abrasive pressure surface. The outer pressure element comprises a rotating wheel (which may be supplied with a cloth, paper, rubber or other yielding surface to preserve the sharpness of the abrasive coated surface) which follows the spiral joint between succeeding convolutions of the abrasive coated strip and applies the pressure as soon as the second strip is in position. Both the strip of splicing material and the abrasive coated strip are supplied to the forming mandrel under sufficient tension to cause the entire surface of the sleeve to accurately conform to the surface of the forming mandrel. Sleeves produced by this new method are distinct from those previously known in that they consist, over the greater part of their area, only of the abrasive coated material used to form them and the area of the splices is only a minor part of the entire area and is of the same thickness and has substantially the same other characteristics, which aifect performance in use, as those of .the principal area of the sleeve.

Another method of forming abrasive sleeves in continuous lengths by use of the splice. of the nature here disclosed is to form such sleeves from a continuous strip of abrasive coated material of suitable width by splicing the opposite edges of such strip to each other. This is readily accomplished by coating'the edges of the strip with adhesive, placing them in abutting relation, with the abrasive surfaces outward, feeding a strip of the splicing material such as metal or glass cloth under the Joint and then applying pressure by suitable means, as for example, a pair of narrow presser rolls one of which is within the tube of abrasive material being formed and in contact with the back surface thereof, and the other being in contact with the outer surface of the abrasive material. The surface of the outer roller is preferably covered with a layer of paper, cloth. rubber or the like to prevent crushing or dulling of the abrasive grains.

Also these abrasive sleeves may be made individually, or in relatively short lengths which can be used as such or cut up into a plurality of tubular pieces, in accordance with this invention. This can be done by forming a sheet of abrasive material into generally tubular forms, with the edges in abuttingrelation, e. g. with the underside of such edges coated with adhesive and a strip of wire screen held in place by the adhesive on one of such edges. The screen can then be embedded in .the backing of both of such edges by the application of mechanical force with any .suitable device. e. g. a mechanical device having a nut cracker type of design. Frequently the simultaneous application of heat is also required.

While our invention is fully described above, its-application in joining abutting edges of sheet abrasive material to form abrasive articles such as belts is illustrated by the appended drawing, in which:

Figure 1 shows, in broken-away section, the two portions of abrasive sheet material generally designated as Iii-l and comprising a backing sheet Ii having one surface coated with a layer of abrasive material l2, adhesively joined to the backing sheet, of which the edges i3-l8 are to be spliced together to form an abrasive article such as a belt or sleeve;

Figure 2 shows the two edges il-IS placed in abutting position and a film or coating of adhesive material I applied on the surface not coated with abrasive.

Figure 3 shows a strip of plicing material. i5 7 applied to the adhesive layer it; and

Figure 4 shows the completed splice. after the application of pressure to th assembly of elements shown in Figure 3, whereby the splicing strip I! has been embedded into the backing ii. Figure 5 shows a plan view of a completed splice in the direction of arrows 5-5 of Figure 4, in which the splice is substantially at, right angles to the length of the strip being spliced and in which a portion has been cut away to'show the various layers or elements.

Figure 61a similar to Figure 5 except that it shows the splice at an angle to the length of the strip.

Figure 'l is similar to Figure 5 except that it shows the abutting edges of the material to be spliced formed in corresponding serrations.

Figure 8 is similar to Figure 5 except that it shows the material to be spliced formed into 1 interlocking areas.

While the new method of forming splices, and

the articles produced thereby, as above disclosed trated our invention in connection with certain specific embodiments. It will be obvious that this invention, and the novel teaching described herein, may be embodied or incorporated in other forms or embodiments. All such variations and embodiments are, of course, contemplated.

What we claim is:

1. An endless abrasive belt of flexible abrasivecoated sheet material comprising a backing sheet and abrasive grains adhesively secured thereto by a coating of binder adhesive, and having a Joint formed by two abutting complementary shaped ends with a metal screen coupling element embedded in the said backing at the end portions and extending longitudinally of the belt between the ends, and which is embedded 'in the said backing on either side of the Joint. thus holding said ends in the said abutting position, and a layer of adhesive on said backing and in contact with said metal screen, the thickness of the end portions of said belt adjacent said joint being substantially uniform and substantially the same as that of the rest of said abrasive belt.

2. In an endless abrasive belt, an improved splice comprised of a wire screen embedded in the backing of said belt at the abutting ends and adhesively retained therein by a phenol-formaldehyde resin, said splice being substantially no thicker than the belt proper.

3. An endless abrasive belt of flexible, abrasivecoated sheet material comprising a fibrous backing and a. coating of abrasive grains adhesively secured thereto, and having a splice formed by two end portions of said belt meeting as a butt joint and having at least one piece of metal screen firmly embedded in the backing of said end portions and extending across the joint formed by the abutting ends thereof, to hold said end portions in said abutting position, said metal screen having an aggregate width approximately that of said abrasive belt and having a length (in the direction of the length of the belt) of the order of about inch to 2 inches, the thickness of said belt at said splice being substantially uniform and substantially the same as that of the rest of said belt, said belt also providing a substantially continuous abrasive coated surface.

4. As a new manufacture, a continuous abrasive band formed of an abrasive coated sheet material and characterized by having a joint wherein two ends of said abrasive coated sheet material are. held together by a narrow strip of metal screen, running in the direction of said joint and overlapping the same and being substantially completely embedded and adhesively retained in the backing material of said abrasivecoated sheet material.

5. As a new manufacture, articles formed from abrasiv coated sheet material by joining edge: thereof together in abutting relation to each other by a plurality of wires of material of high tensilestrength relative to said sheet material,

said abrasive coated sheet material being substantially the full thickness thereof at said abutting edges thereof and said .wires extending across said edges and being embedded in th backing of said abrasive coated sheet material and adhesively retained therein on opposite sides of the proximate edges aforesaid.

6. An endless band of abrasive coated sheet material having an improved splice in which proximate abutting edges of said sheet material are held together by a wire screen which overlaps said edges and is embedded and adhesively retainedinthe backing of said abrasive icoated sheet material on opposite sides of and adjacent to said edges, said splice being substantially no thicker than the belt proper.

7. As a new manufacture, an endless abrasive belt of flexible abrasive-coated sheet material characterized by having a joint wherein two abuts ting complementary shaped ends thereof are held together by a wire screen coupling element, said wire screen overlapping said abutting ends and being substantially completely embedded and adhesively retained in the backing material of the abrasive coated sheet material.

8. As a new manufacture, an endless abrasive belt of flexible abrasive-coated sheet material comprising a backing sheet having a layer or coating of abrasive grits bonded thereto. characterized by having a joint wherein two abutting complementary shaped ends thereof are held together by a multiplicity of wires which overlap said abutting ends and are substantially completely embedded in said backing sheet and adhesively retained therein said abrasive coated sheet material being substantially the full thickness thereof at said joint.

9. As a new manufacture, a continuous abrasive band formed of a strip oi'abrasive coated sheet material comprising a backing having a layer of abrasive grits bonded thereto, characterized by having a joint wherein two ends of said strip are held in abutting relation by a coupling member of open mesh sheet material comprisingwires of high tensile strength, said coupling member overlapping said ends and being embedded and adhesively retained in said backing adjacent said ends.

10. An abrasive article of flexible abrasivecoated sheet material comprising a backing sheet and abrasive grains adhesively secured to a surface thereof by a coating of binder adhesive. and having a joint formed by two abutting edges or said sheet material retained in said abutting position relative to each other by a coupling element of open mesh sheet material formed of threads of a material of high tensile strength relative to the backing sheet of said abrasive-coated sheet material and embedded and adhesively retained in said backing sheet on either sid of the joint. the thickness of the edge portions of said abrasive article adjacent said joint being substantially uniform and substantially the same as that of the rest of said abrasive article.

11. The method of splicing abrasive coated sheet material comprising a flexible backing and a layer of abrasive grits bonded to said backing by a coating of binder adhesive, which includes the steps of bringing the edges of said abrasive material into abutting relation to form a joint, applying an adhesive to said backing adjacent to and on either side of said joint, applying a plurality of wires to said adhesive so as to extend across said joint, and then applying pressure to embed said wire in said backing.

12. In an endless abrasiv belt, an improved splice comprised of a wire screen embedded in the backing of said belt at the abutting ends and adhesively retained therein, said splice being substantially no thicker than the belt proper.

13. A tubular or cylindrical abrasive sleeve formed of an abrasive coated sheet material having a joint extending longitudinally of said sleeve formed by two abutting edges of said sheet material retained in said abutting position relative to each other by a coupling element of open mesh material formed of threads of a material of high tensile strength relative to the backing sheet of said abrasive coated sheet material and embedded and adhesively retained in said backing sheet on either side of the joint, the thickness of the abrasive sheet materialat and adjacent said joint being substantially uniform and substantially the same as that of the rest of said abrasive article.

14. An endless abrasive belt characterized by having an improved splice comprised of an open mesh glass cloth embedded in the backing of said belt at the abutting ends thereof and adhesively retained therein, said splice being substantialLv no thicker than the belt proper.

15. An abrasive article of flexible abrasive coated sheet material comprising a backing sheet and abrasive grains adhesively secured to a surface thereof by a coating of binder adhesive, and having a joint formed by two abutting edges-of said sheet material retained in said abutting position relative to each other by an open mesh glass cloth embedded and adhesively retained in said backing sheet on either side 0! the oint, the thickness of the edge portions of said abrasive article adjacent said joint being substantially uniform and substantially the same as that o! the rest of said abrasive article.

16. As a new manufacture, a continuous abrasive band formed of abrasive coated sheet material comprising a backing sheet having a layer or coating of abrasive grains bonded thereto, characterized by having a joint wherein two ends of said abrasiv coated sheet material are held together in abutting relation by a multiplicity of threads of such a material that said threads are substantially non-deformable in their cross-sectional dimension, said threads of material over- 4 

